This invention pertains to fire protection sprinkler systems and more particularly pertains to an adjustable drop nipple for use with sprinkle head assemblies of the dry, pendant type, i.e. systems which contain a compressed gas such as air until such time as the sprinkler heads operate, and wherein the sprinkler head assemblies extend downwardly to a finished ceiling line from a distribution network which supplies a fire extinguishing fluid to the sprinkler heads in the event of a fire.
When suspending sprinkler heads from a distribution system for alignment with a dropped ceiling, the drop nipples for the heads cannot all be cut to the same length if precise alignment of each head with the ceiling is to be accomplished. Such alignment problems result from the fact that neither the distribution system nor the ceiling below it can be installed perfectly level, so that the vertical distance between the two is subject to significant variation. It is thus not possible to precut the drop nipples to correct lengths prior to installing the ceiling, and such is difficult and time consuming once the ceiling is in place. In addition, either or both of the ceiling and the distribution system can be disturbed and rendered unlevel even after installation thereof by settling and shifting of a building in which they are installed.
Adjustable drop nipples for sprinkler heads have been devised which comprise telescoping lengths of conduit whereby the overall length of the assembly can be adjusted by moving a lower conduit axially within an upper, stationarily mounted conduit to arrive at a selected drop length that is then maintained by means which prevents further axial movement of the lower conduit. Such adjustable drop nipples are disclosed, for instance, in U.S. Pat. Nos. 3,529,671; 3,675,952 and 3,807,503. As can be seen therein, the selected drop length of the nipple is adjusted and maintained by turning threaded elements such as an adjusting screw or the lower conduit of the telescoping assembly itself, or by axially sliding the lower conduit within the upper conduit and then locking it in place with threaded rollers. These prior adjustable drop nipples have not proven altogether satisfactory for one reason or another, including complex and expensive construction, lack of rigidity and difficulty of sealing between the walls of the upper and lower conduits, and unacceptable time requirements for installation.